The present disclosure relates to circuitry for use with the ignition of gas discharge lamps and particularly to circuitry employing an electronic ballast with circuitry for interfacing with ballast with a remote controller operative for effecting dimming of the gas discharge lamps. Presently, it is common practice to house the ballast circuitry and interface circuitry in a common housing with a set of electrical leads extending therefrom for connection to a power line such as a 120 volt/240 volt single phase AC line and another set of electrical leads for outputting a low voltage low operage signal to the dimming controller.
In service, there has been encountered instances where, despite appropriate color coding of each set of electrical leads, the low voltage signal leads intended for connection to the controller have been miswired and connected to a line voltage power source. The connection of the low voltage interface circuit leads to the line power has resulted in an over current condition and burn out of the electronic ballast circuitry.
Heretofore, attempts to protect the ballast interface circuitry and ballast against over voltage have utilized a positive temperature coefficient or PTC thermistor which responds to the higher voltage by heating and increasing the resistance thereby reducing the current flow in the interface circuit. The PTC is operable to return to its lower or cold resistance state when the overvoltage is removed thereby enabling resumption of the low voltage operation with the remote controller. However, where the circuitry is encased in a potting compound, it is necessary to isolate the PTC from the potting compound to protect the potting compound from the elevated temperatures generated by the PTC in the event of miswiring. This has resulted in added cost due to the necessity of rearranging the circuitry to isolate the PTC.
Thus, it has been desired to find a simple and relatively low cost technique for protecting the controller interface circuitry employed with an electronic ballast for a gas discharge lamp from miswiring by connecting the low voltage controller leads to a high voltage power line.